FR2711943A1 - Guided knife device for bag making machine. - Google Patents

Abstract

The guided knife sheet cutting apparatus uses an arm (32) adjustable to support the cutting head (34) containing the blade. The cutting head is moved by a control motor driving an arm (32) which moves the knife containing the blade along the guide track (30) in order to perform complex cuts of the sheet.

Description

GUIDED KNIFE DEVICE FOR BAG MANUFACTURING MACHINE

  The present invention relates to bag making machines of the type producing plastic bags from a plastic sheet at high production speeds. The particular invention presented here is a knife guided by rails which can cut segments in a series of bags during the continuous bag manufacturing process. The

  knife cuts two adjacent bags in one pass.

  More specifically, the invention relates to a knife assembly intended for use in cutting the selvedge of a plastic sheet bag while said bag is being manufactured, said selvedge comprising a curved part and a non-curved part. comprising: clamping means for retaining said sheet during a cutting operation; a rotary drive mechanism; a knife arm which can be moved by said rotary drive mechanism over an arc of more than 180 degrees; a knife support carriage pivotally attached to an outer end of said knife arm; a knife blade, mounted on said knife support carriage, having a cutting portion on its two sides allowing said knife to cut said sheet when said knife moves in a first or a second direction; guide cams mounted on said knife support carriage; a way to allow contact with said guide cams and maintain said knife support carriage in a position prescribed by said way when said knife arm is moved by said following rotary drive mechanism

said arc.

  The invention also relates to a method for cutting the edge of a plastic bag using a knife mounted on a knife support carriage, said carriage being mounted at the outer end of a cutting arm, while said bag is being manufactured, comprising the following steps: positioning a said first plastic bag in a position to be cut; switching on said cutting arm so that said cutting arm moves in an arc of at least 180 degrees while said knife is in contact with said plastic bag so as to cut its selvedge; parking said cutting arm in a 180 position

  degrees at least from its starting point.

  In other words, the invention presented here is a system for supporting a knife with the system comprising the invention. The system includes a set of rails and a set of cams attached to the knife holder. The cams guide the support

  knife along rails to facilitate cutting the sheet.

  The knife holder is supported by an arm or rod which is controlled by a motor to be moved in a first direction

then in the opposite direction.

  The bag which is produced using this device is a "handle bag" and more specifically a handle part of a patterned bag. Patterned plastic bags are widely used to package packages of pre-folded pattern consumer items often made from paper products. The pre-folded designs are compressed into generally rectangular packages which may be difficult for a customer to carry without the handle which is

  often formed in one piece with the patterned bag.

  Such bags are made on machines for making bags in continuous operation from a sheet coming from a support containing a sheet reel. The sheet can be folded, provided with bellows, perforated, punched and welded at various stations of the bag making machines in a well known manner. A station can be used to cut the selvedge adjoining the handle part of the bag. In the known devices, this cutting can be carried out by several methods such as those using a serrated knife, a knife

  flying on a heated belt or knife.

  The serrated knife, which was generally used for a punching operation, did not give a clean and beautiful cut but left a rather serrated edge which of the

  aesthetic point of view is undesirable.

  Flying knives are complex and to cut a shape different from that defined, the complete flying knife must be replaced. The system presented here, which cuts parts of two adjacent bags simultaneously, includes a knife mounted on a carriage or a knife holder. The carriage follows rails which follow the path determining the shape to be cut. The carriage is driven by a swivel arm which is driven by a mechanism

  rotary drive as explained below.

  An advantage of this invention is that the knife cuts in a first and a second direction allowing it to make a single stroke per machine cycle without requiring a

return stroke without cut.

  This advantage and the other advantages of the invention

  will be well understood by reading the following description and by

  looking at the drawings in which identical reference numerals identify identical elements and in which FIG. 1 is a plan view of the environment of the invention in a simplified presentation; Figure 2 is a plan view showing the invention in more detail; Figure 3 is a side elevational view of the accessory mounted for manufacturing; Figure 4 is a partial cross-sectional part of the knife holder and the carriage along plane 4-4 of Figure 3; Figure 5 is a part in partial cross section of the knife holder and the carriage of Figure 3 side view in elevation;

  Figure 6 is a view of the invention along the plane 6-

  6 of Figure 5; Figure 7 is an alternative embodiment of the invention; Figure 8 is an alternative embodiment of the invention. Referring now to the drawings, one of the embodiments of the invention is shown in Figure 1. This figure also shows the general embodiment 10 of the invention which will be well understood by those familiar with the manufacture of plastic bags on machines & make them

  high speed and continuously developing bags.

  In this figure, several parts of bags are shown. For example, a front bag, which is attached to a perforation of a previous front bag, is attached to a perforation

  or joint 20 of a rear bag 14. In the description which follows,

  it is practical to treat these bags as finished bags with the exception of the end of the separation of the bags between them and the cutting of the selvedge between the handle part 16 of the bags. The

  bags include a body portion 24 and a bottom edge 22.

  In this embodiment, the bags move from right to left during the process, as indicated by arrow A. Article 26 is the cutting assembly and its guide system. FIG. 1 shows an arm 32 of the cutting system, a knife support carriage 34, a guide system with slide or rails 30 having side walls 76 and 104 of unconnected guide comprising a straight part 44 between a first curved part 42 and a second curved part 46. Although the details of the structure are developed below, the cut 18 is formed when the arm 32, pivoting on the pivot point 38 sweeps the arc defined by the path 30. The sheet is securely held by a fastening system to help achieve a clean cut. The arm cuts in both directions making a cut in each direction then, after the series of bags has been located at the new spacing between handles, the knife is recycled in the opposite direction and makes a cut for

  its return to the rest point shown in Figure 1.

  In FIG. 1, the knife support and guide carriage 34 is fixed to the end of the arm 32 which, in this embodiment, is a pair of rods which are slidably supported in the block 36, and the internal ends of the arms are variable so that the radius between the pivot point 38 and the position of the guide carriage 34 is adjustable while

the carriage follows the rails 30.

  In FIG. 2, an alternative embodiment is presented. It is similar to the apparatus shown in FIG. 1, the difference being that the knife support and guide carriage 34a is not fixed to the end of the arm 32a but is movable inside and outside on arm 32a, while at

  the inner end of the arm 32a, the block 36a is fixed to the arm.

  Figures 3 and 4 describe the details of the functional assembly generally presented in Figures 1 and 2. The sheet 66 in these views is shown between a lower clamping plate 70 and an upper guide support 74. The lower clamping plate 70, by means of clamping cylinders such as 72, block the sheet 66 between the upper guide support 74 and itself. The sheet is also held stationary so that the knife 64 can cut the sheet 66 clearly

  to remove the selvedge or cutout 18.

  The knife 64 is equipped with cutting edges 64a and 64b to allow it to cut the sheet in a first or a second direction as explained above. The knife 64 is held in the knife holder and guide carriage 34, which also includes attachment points for the first tubular or rod-shaped arm 50 and the second tubular or rod-shaped arm 52. A carriage base 60 is integral with the knife support and guide carriage 34 and provides a mounting base for the pair of rollers or cams 56 and 58 which are mounted so as to have a rotary movement on the axes supported by the carriage base 60. The cams 56 and 58 remain between the side walls 76 and 104 of said track 30. The carriage base 60 is also the direct point of attachment of the knife 64. The carriage base 60 is rotatably mounted via the pivot point 54 on the main body 48 so that the carriage base 60 can pivot independently of the part 34 which is integral with the main body 48 and is held in a fixed position by means of its fixed attachment, in the embodiment rep resented

  in FIG. 3, on the arm 32 (composed of the rods 52 and 50, fig. 4).

  The arm 32 is mounted through the central box 36 in such a way that it allows the arm to modify its actual radius by means of the sliding of the rods 50 and 52 through openings, in fact oblong holes in the central box. The central box 36 is mounted in the axial direction by means of a central box with an axis 40 pivoting on a pivot point such as 38 which acts as an axis. By observing FIGS. 1 and 3, it can be seen that the arm 32 can be forced transversely & through the central box 36 in response to the cams 56 and 58 along the rails 30. The track going from a curved part 42 through the part straight 44 and in the curved part 46, the actual radius between the knife 64 and the pivot point of the axis 38 is therefore variable. The arm 32 or the rods 52 and 50 moving through the central box 36 adapt to the change of radius and let the knife follow the

path imposed by the rails 30.

  The knife performs a first movement being driven by a rotary control mechanism 28 which can be a means of electric, pneumatic or hydraulic motor, as the case may be, for moving the arm over an arc of about, and slightly greater than, 180 degrees, in looking at Figure 1 clockwise and to make the cut such as 18 in the front bag 12 (performing a rear cut) and in the rear bag 14 (performing the front cut). The knife and arm then park in a position 180 degrees from their starting point until the next set of uncut and connected bags is located in the area where the edge cut is formed. When the next set of bags is identified, the knife makes a second movement, this time anticlockwise and performs the cut such as 18 in the rear bag (making the front cut) and in the front bag (performing the rear cutout). The knife and the arm will then park as in Figure 1 and wait until the bags are located at

  the perforation where the cycle is repeated.

  Figures 5 and 6 show an alternative embodiment of the invention. In this embodiment, only a single rail or a single erected wall 76 having two sides is used to guide the knife 64. The track 76 has two rollers or cams 56 and 58 on one side of the track 76. The cams 56 and 58 are fixed to the carriage base 60 in a rotary manner similar to the cams 56 and 58 of FIG. 1. However, the third cam 62 is installed on a support 80 loaded by spring which pivots around the pivot point (screw) 82 and is brought into engagement with the track 76 by means of the spring 88. The guide groove 84 and the guide 86

contain the cam holder 80.

  The knife apparatus 64 is similar to that shown

  in Figure 1 and the functional cycle is as described below

  above. The only difference is the use of three cams operating on and guided by a single track of rails instead of two cams operating between two guide rails as

shown in figure 1.

  Figure 7 shows another embodiment of the invention. In this embodiment, an arm 32b is equipped with an oblong opening 94 which allows the roller of the groove 96 to move inside and outside on the arm as the arm advances along the rails. The roller of the groove 96 can advance upwards from the carriage and include the pair of cams 56 and 58 and the knife 64 as shown in FIG. 4. The difference here is that the carriage is not fixed to the outer end of the arm but is free to move. The inner end of the arm is fixed so that all the radial loads are exerted by the carriage

moving on the arm.

  Figure 8 shows an enlarged view of the device shown in Figure 7 with a slight difference in the shape of the arm 32c. Functionally, there is no difference between

  the apparatus of FIG. 7 and that of FIG. 8.

  The previous description tries to expose several

  embodiments of the invention, the preferred embodiment being the embodiment of FIG. 1. It is obvious to anyone specializing in the technique of bag making machines that design nuances and combinations of the embodiments

  exposed here are possible. The appended claims try

  to claim these nuances of design on a proportionate field

to their extent.

Claims (10)

Claims:   1. Knife assembly for use in cutting the selvedge (18) of a sheet bag (66) of plastic while said bag is being manufactured, said selvedge (18) comprising a curved portion and a non-curved portion comprising: clamping means (70, 72) for retaining said sheet (66) during a cutting operation; a rotary drive mechanism (28); a knife arm (32, 32a, 32b, 32c) which can be moved by said rotary drive mechanism (28) over an arc of more than 180 degrees; a knife carriage (34, 34a) (64) pivotally attached to an outer end of said knife arm (32);   a knife blade, mounted on said knife support carriage (34, 34a), having a cutting part on its two sides allowing said knife to cut said sheet (66) when said knife (64) moves in a first or a second direction; guide cams (56, 58) mounted on said knife support carriage (34, 34a); a track (30) for allowing contact with said cams (56, 58) to guide and maintain said knife support carriage (34, 34a) in a position prescribed by said track (30) when said knife arm (32) is moved by said mechanism   rotary drive (28) along said arc.   2. Assembly according to claim 1 characterized in that said channel (30) comprises two unconnected side walls (76, 104) and said cams (56, 58) remain between said   side walls (76, 104) of said track (30).   3. An assembly according to claim 2 characterized in that said cams include a first (56) and a second (58) cam. 4. The assembly of claim 2 characterized in that said track comprises a single wall (76) erect and at least one of said cams (56, 58) is in contact with one of the faces of said wall (76) erected.   5. Assembly according to claim 2 characterized in that said knife arm (32) is supported on a central housing (36).   6. An assembly according to claim 5 characterized in that said knife arm (32) can move in one direction   transverse through said central housing (36).   7. The assembly of claim 5 characterized in that said knife arm (32) is fixed to said central housing (36) and said knife support carriage (34) can move in a   transverse direction along said knife arm (32).   8. An assembly according to claim 5 characterized in that said knife arm (32) is composed of two rods (50, 52) extending from said central housing (36) to said support carriage knife (34).   9. An assembly according to claim 5 characterized in that said knife arm (32) is provided with an opening capable of   receiving a cam from said knife support carriage (34).   10. Assembly for cutting the edge of a plastic bag using a knife (64) mounted on a knife support carriage (34), said carriage (34) being mounted at the outer end of a cutting arm (32), while said bag is being manufactured, comprising the steps of: positioning said first plastic bag in a position to be cut; switching on said cutting arm (32) so that said cutting arm (32) moves in an arc of at least degrees while said knife (64) is in contact with said plastic bag so as to cut its edge (18); parking said cutting arm (32) in a position at   degrees at least from its starting point.